The present invention generally relates to laser drilling, and particularly relates to a method for milling repeatable exit holes in ink jet nozzles.
Material ablation by pulsed light sources has been studied since the invention of the laser. Etching of polymers by ultraviolet (UV) excimer laser radiation in the early 1980s led to further investigations and developments in micromachining approaches using lasersxe2x80x94spurred by the remarkably small features that can be drilled, milled, and replicated through the use of lasers. A recent article entitled xe2x80x9cPrecise drilling with short pulsed lasersxe2x80x9d (X. Chen and F. Tomoo, High Power Lasers in Manufacturing, Proceedings of the SPIE Vol. 3888, 2000) outlines a number of key considerations in micromachining. Other recent patents of interest include the following:
U.S. Pat. No. 6,260,957, xe2x80x9cInk jet printhead with heater chip ink filter,xe2x80x9d describes a silicon ink filter for a heater chip of an ink jet printhead that is formed by micromachining and laser drilling. The heater chip may contain a plurality of such filters for the plurality of nozzles of the printhead. The filter has a via constituting an ink entrance area formed by micromachining and a plurality of bores formed at the exit side of the via produced by laser drilling. Protective layers are preferably disposed over the heater chip substrate prior to micromachining and laser drilling.
U.S. Pat. No. 6,089,698, xe2x80x9cNozzles and methods of and apparatus for forming nozzles,xe2x80x9d describes nozzles for an ink jet printer formed by laser ablation in a nozzle plate that has previously been bonded to the body of the printer. The laser beam is caused to converge at a point in front of the nozzle plate so that a nozzle is formed which tapers toward the outlet. First and second beam masks are established in front of a focusing lens with the masks being respectively conjugate in the lens with the nozzle inlet and outlet, which are of different shape. The nozzle has a central land that controls the ink meniscus and avoids the ejected drop receiving a sideways kick from the nozzle wall.
U.S. Pat. No. 6,023,041, xe2x80x9cMethod for using photoabsorptive coatings and consumable copper to control exit via redeposit as well as diameter variance,xe2x80x9d describes a method of forming a through-via in a laminated substrate by applying a polymeric photo-absorptive layer on an exposed bottom surface of a laminated substrate. A through-via is laser drilled in the substrate from a top of the substrate through the substrate to a bottom of the substrate. The photo-absorptive layer formed on the bottom surface of the substrate is then removed.
European Patent No. EP0867294, xe2x80x9cInk jet printhead nozzle plates,xe2x80x9d describes a method for making an inkjet printhead nozzle plate from a composite strip containing a nozzle layer and an adhesive layer. The adhesive layer is coated with a polymeric sacrificial layer prior to laser ablating the flow features in the composite strip. A method is also provided for improving adhesion between the adhesive layer and the sacrificial layer. Once the composite strip containing the sacrificial layer is prepared, the coated composite strip is then laser abated to form flow features in the strip in order to form the nozzle plates. After forming the flow features, the sacrificial layer is removed. Individual inkjet printhead nozzle plates are separated from the composite strip by singulating the nozzle plates with a laser.
U.S. Pat. No. 5,548,894, xe2x80x9cInk jet head having ink-jet holes partially formed by laser-cutting, and method of manufacturing the same,xe2x80x9d describes a method of manufacturing an ink jet head including an ink-chamber member having ink chambers, and a nozzle plate secured to a front end face of the ink-chamber member and which has ink-jet holes communicating with the respective ink chambers, wherein a blank for the nozzle plate is formed by injection molding, such that blind holes are formed in one of opposite surfaces of the blank and such that each blind hole has a varying-area portion whose cross sectional area decreases in a direction from the above-indicated one of opposite surfaces of the blank toward the other surface, and the blank is subjected to laser-cutting to prepare the nozzle plate having orifice holes which cooperate with the blind holes to form the ink-jet holes. The size of each blind hole at an open end thereof is preferably smaller than the size of the ink chamber at an end thereof at which the ink chamber communicates with the ink-jet hole.
Ultrafast lasers generate intense laser pulses with durations from roughly 10xe2x88x9211 seconds (10 picoseconds) to 10xe2x88x9214 seconds (10 femtoseconds). Short pulse lasers generate intense laser pulses with durations from roughly 10xe2x88x9210 seconds (100 picoseconds) to 10xe2x88x9211 seconds (10 picoseconds). Along with a wide variety of potential applications for ultrafast and short pulse lasers in medicine, chemistry, and communications, short pulse lasers are also useful in milling or drilling holes in a wide range of materials. In this regard, hole sizes in the sub-micron range are readily drilled by these lasers. High aspect ratio holes are also drilled in hard materials; applications in this regard include cooling channels in turbine blades, nozzles in ink-jet printers, and via holes in printed circuit boards.
Creation of a repeatable hole shape that meets stringent specifications is frequently critical in quality control for manufacturing applications. Laser systems are flexible in meeting such specifications in milling because appropriate programming can easily engineer custom-designed two-dimensional (2D) and three-dimensional (3D) structures and translate such designs into numerical control of the laser in real-time. However, as the required feature size for these structures decreases, mass production of quality micromachined products becomes more difficult to conduct in a rapid, cost-effective manner that consistently meets product specifications.
Key factors in inkjet printer quality derive from inkjet nozzle design, construction techniques, and operation. Nozzle design defines a need for a number of holes to be milled in the aforementioned materials. Each nozzle hole includes a shaped section and an exit hole. The exit hole is critical in controlling ink ejection from an inkjet printer nozzle. Inconsistent expulsion of ink leads to poor print quality; therefore, imperfections in the exit hole negatively impact print quality.
Manufacturers of inkjet printers require that inkjet nozzle holes meet specific workpiece geometry. The measurements (e.g., input diameter, exit diameter, depth of exit hole, and taper angle) of the hole and shape of the hole (e.g., tapered with cylindrical exit hole) are critical to the product quality and the operation of the end application. In addition, inkjet nozzle manufacturing must provide manufacturing methods of laser tool operation, material controls, and inspection to achieve repeatable size and shape to ensure consistency among mass-produced nozzles.
Although laser drilling inkjet nozzles provides numerous advantages and benefits over other drilling methods, defects in the final product remain a problem. Current laser drilling systems, such as those using picosecond lasers, still create defects, such as burrs and notches, in the finished product. These defects are particularly detrimental in the exit hole because the size and smoothness aspects of the exit hole are critical to acceptable inkjet nozzle performance. Burrs or notches cause restrictions in the high velocity expulsion of inks and cause variability in the position and amount of ink per dot; burrs and noteches therefore diminish print quality. Many current laser drilling techniques utilizing short pulse, low energy lasers use traditional trepanning (e.g. cutting a circular pattern to remove a core, leaving a hole) to create the exit hole. This trepanning method causes an unpredictable notch or burr to be formed in the otherwise cylindrical exit hole. As previously noted, this notch or burr is undesirable because of its negative impact on print quality. What is needed is a way to minimize these defects in laser drilling inkjet nozzles to enhance quality and consistency in manufactured inkjet nozzle. The present invention provides a solution to this need.
According to the present invention, a method of laser milling an aperture in a workpiece for use with manufacturing ink-jet nozzles includes initially illuminating a surface of the workpiece with a laser beam at a point within an outer perimeter of a desired aperture and a distance away from the outer perimeter sufficient to substantially avoid initial ablation of the outer perimeter. The laser beam is driven substantially in the direction of the outer perimeter at a variable rate controlled to avoid deformation of the outer perimeter. Material of the workpiece is ablated in a pattern designed to substantially remove material within the outer perimeter, thereby forming the aperture.
A number of advantages are provided with the invention. Print quality in inkjet printers is generally improved even as quality and consistency in manufacturing inkjet nozzles is also improved. Defects in laser drilling inkjet nozzle holes are minimized. The elimination of notching provides for repeatable exit holes in inkjet nozzles. The method and system of the present invention also add little cost to the manufacturing of inkjet nozzles insofar as the method can be implemented using currently-deployed systems and additional tools to the conventional components of a laser drilling system are not required in many cases.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.